Children's teeth begin forming before birth. Around 6 months, the first primary (or baby) teeh to erupt through the gums are the lower central incisors, followed closely by the upper central incisors. All 20 primary teeth usually appear by age 3. Permanent teeth begin appearing around age 6, starting with the first molars and lower central incisors. This process continues until approximately age 21. Adults have up to 32 teeth including the third molars (or wisdom teeth)